http://national-geographic.cafepress.com/art/s_1389324/2011/05/great-barrier-reef/img/15-opal-reef-714.jpg/2011/05/great-barrier-reef/img/reef-60-15.jpgPhotograph by David Doubilet

Acropora species, vie for space and energy-giving sunlight off Cairns. Though highly vulnerable to changing sea chemistry, these master builders of Indo-Pacific reefs have persisted for millions of years.